Iron-based ODS (oxide-dispersion-strengthened) materials, for example ferritic ODS FeCrAl alloys, have been known for some time. On account of their outstanding mechanical properties at high temperatures, they are, for example, used for components that are subjected to extreme thermal and mechanical stress, such as gas turbine blades or vanes.
These materials can also be used for tubes to protect thermocouples which are used, for example, in gas turbines with sequential combustion for temperature control and are exposed to extremely high temperatures and oxidizing atmospheres.
Table 1 specifies nominal chemical compositions (in % by weight) of known ferritic iron-based ODS alloys:
TABLE 1Nominal composition of known ODS-FeCrAlTi alloysAddition of reactiveelements (in theAlloyConstituentform of an oxidedesignationFeCrAlTiSidispersion)KanthalRem.20.05.50.030.23ZrO2—Al2O3APMMA 956Rem.20.04.50.5—Y2O3—Al2O3 (0.5 Y2O3)PM 2000Rem.19.05.50.5—Y2O3—Al2O3 (0.5 Y2O3)
The operating temperatures of these metallic materials reach up to, for example, approximately 1350° C. They have potential properties that are more typical of ceramic materials.
The materials mentioned can have very high creep rupture strengths at very high temperatures and can also provide outstanding high-temperature oxidation resistance by forming a protective Al2O3 film, as well as a high resistance to sulfidizing and vapor oxidation. They can have highly pronounced directional-dependent properties. For example, in tubes, the creep strength in the transverse direction is approximately 50% of the creep strength in the longitudinal direction.
ODS alloys of this type are produced by powder metallurgical processes, using mechanically alloyed powder mixtures that are compacted in a known way, for example by extrusion or by hot isostatic pressing. The compact is subsequently highly plastically deformed, usually by hot rolling, and subjected to a recrystallization annealing treatment. This type of production, but also the material compositions described, results in, inter alia, these alloys being very expensive and having anisotropic properties.
Furthermore, various Ni-based wrought alloys such as, for example, Hastelloy X and Haynes 214 are known, and can be produced at a lower cost than the materials mentioned above and do not have anisotropic properties. These alloys have the following chemical compositions:
TABLE 2Nominal composition of known Ni-based wrought alloysAlloydesig-ConstituentnationNiCrCoMoWFeMnSiCAlYHastelloyRem.221.590.618.50.50.50.10.3—XHaynesRem.16———3——0.044.50.01214
According to the company brochure, the material Haynes 214 should be the most oxidation-, carburization- and chlorination-resistant alloy commercially available as a wrought alloy, with effective use being possible at 2200° F. (approximately 1205° C.) for long-term stress and at 2400° F. (approximately 1316° C.) for short-term stress. However, properties of this alloy at very high temperatures are not as good as the outstanding properties of the ODS alloys mentioned above.